The present invention relates generally to printers and, more particularly, to a method for reducing the effect of paper feed errors on the visual quality of printed images.
Printers such as inkjet printers typically include a paper indexing mechanism such as a paper feed roller the movement of which may be controlled by a motor through a gear arrangement. During a printing operation paper is moved or indexed along a paper path, stopped and then a print head carriage is moved across the paper path to eject ink onto the paper. The paper is indexed again, stopped and the print head carriage is again moved across the paper path. If an error occurs in the indexing, the resulting position of ink on the paper will be off slightly from the intended or desired position, which can result in undesired banding in the resultant printed image. Because the banding tends to be uniform and horizontal across the width of the paper, the banding tends to be visible in the resultant printed image. In the past a technique known as xe2x80x9cshinglingxe2x80x9d has been reduced to introduce some randomness in the printer image in order to reduce the effect of indexing errors. Shingling involves the use of multiple printing scans during which image pixels are overlapped. However, shingling increases throughput time for a given printed image by increasing the number of printing scans required.
Accordingly, it would be advantageous to provide a technique for reducing banding caused by paper feed/indexing errors in ink jet printers.
In one aspect, a method for reducing horizontal banding on media in an ink jet printer involves the step of moving the media repeatedly back and forth along a media movement path during a printing scan of at least one print head, the printing scan defined by movement of the print head across the media movement path as ink is ejected from the print head onto the media.
In another aspect, a printing method for an ink jet printer involves the steps of: (a) moving a media along a media movement path of the printer into a first printing position range, (b) performing a first printing scan of a print head, the first printing scan defined by movement of the print head across the media movement path as ink is ejected onto the media from the print head; and (c) during the first printing scan, moving the media repeatedly back and forth along the media movement path and within the printing position range. The aforementioned method may involve the further steps of (d) moving the media along the media movement path into a second printing position range; (e) performing a second printing scan of the print head, the second printing scan defined by movement of the print head across the media movement path as ink is ejected onto the media from the print head; and (f) during the second printing scan, moving the media repeatedly back and forth along the media movement path and within the second printing position range.
In a further aspect, an ink jet printing system includes a paper movement path and a print head carriage mounted for movement across the paper movement path and having at least one print head mounted thereon. A paper indexing arrangement includes a paper feed roller, a motor operatively coupled for rotating the paper feed roller, an encoder operatively connected for producing output signals indicative of paper feed roller position and a motor drive control connected to control energization of the motor, the motor drive control receiving the output signals of the encoder. During a printing scan defined by movement of the print head carriage across the paper movement path as ink is ejected from the print head onto paper, the motor drive control controls energization of the motor for repeatedly varying a rotation direction of the paper feed roller in order to repeatedly move the paper back and forth along the paper movement path.
In yet another aspect, an ink jet printing system includes a paper movement path and a print head carriage mounted for movement across the paper movement path and having at least one print head mounted thereon. A paper indexing arrangement includes a paper feed roller, a motor operatively coupled for rotating the paper feed roller, and a motor drive control connected to control energization of the motor. During a printing scan defined by movement of the print head carriage across the paper movement path as ink is ejected from the print head onto paper, the motor drive control controls energization of the motor for repeatedly varying a rotation direction of the paper feed roller in order to repeatedly move the paper back and forth along the paper movement path.